'\" te
.\" Copyright (c) 2009 Sun Microsystems, Inc. All Rights Reserved.
.\" Copyright 1989 AT&T
.\" Copyright (c) 1983 Regents of the University of California.  All rights reserved.  The Berkeley software License Agreement  specifies the terms and conditions for redistribution.
.TH GETITIMER 2 "Jun 15, 2009"
.SH NAME
getitimer, setitimer \- get or set value of interval timer
.SH SYNOPSIS
.LP
.nf
#include <sys/time.h>

\fBint\fR \fBgetitimer\fR(\fBint\fR \fIwhich\fR, \fBstruct itimerval *\fR\fIvalue\fR);
.fi

.LP
.nf
\fBint\fR \fBsetitimer\fR(\fBint\fR \fIwhich\fR, \fBconst struct itimerval *\fR\fIvalue\fR,
     \fBstruct itimerval *\fR\fIovalue\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The system provides each process with four interval timers, defined in
<\fBsys/time.h\fR>. The \fBgetitimer()\fR function stores the current value of
the timer specified by \fIwhich\fR into the structure pointed to by
\fIvalue\fR. The \fBsetitimer()\fR function call sets the value of the timer
specified by \fIwhich\fR to the value specified in the structure pointed to by
\fIvalue\fR, and if \fIovalue\fR is not \fINULL\fR, stores the previous value
of the timer in the structure pointed to by \fIovalue\fR.
.sp
.LP
A timer value is defined by the \fBitimerval\fR structure (see
\fBgettimeofday\fR(3C)) for the definition of \fBtimeval\fR), which includes
the following members:
.sp
.in +2
.nf
struct timeval    it_interval;         /* timer interval */
struct timeval    it_value;            /* current value */
.fi
.in -2

.sp
.LP
The \fBit_value\fR member indicates the time to the next timer expiration. The
\fBit_interval\fR member specifies a value to be used in reloading
\fBit_value\fR when the timer expires. Setting \fBit_value\fR to 0 disables a
timer, regardless of the value of \fBit_interval\fR. Setting \fBit_interval\fR
to 0 disables a timer after its next expiration (assuming \fBit_value\fR is
non-zero).
.sp
.LP
Time values smaller than the resolution of the system clock are rounded up to
the resolution of the system clock, except for  \fBITIMER_REALPROF\fR, whose
values are rounded up to the resolution of the profiling clock. The four timers
are as follows:
.sp
.ne 2
.na
\fB\fBITIMER_REAL\fR\fR
.ad
.RS 19n
Decrements in real time.  A \fBSIGALRM\fR signal is delivered to the process
when this timer expires.
.RE

.sp
.ne 2
.na
\fB\fBITIMER_VIRTUAL\fR\fR
.ad
.RS 19n
Decrements in lightweight process (lwp) virtual time. It runs only when the
calling lwp is executing. A \fBSIGVTALRM\fR signal is delivered to the calling
lwp when it expires.
.RE

.sp
.ne 2
.na
\fB\fBITIMER_PROF\fR\fR
.ad
.RS 19n
Decrements both in lightweight process (lwp) virtual time and when the system
is running on behalf of the lwp.  It is designed to be used by interpreters in
statistically profiling the execution of interpreted programs. Each time the
\fBITIMER_PROF\fR timer expires, the \fBSIGPROF\fR signal is delivered to the
calling lwp. Because this signal may interrupt in-progress functions, programs
using this timer must be prepared to restart interrupted functions.
.RE

.sp
.ne 2
.na
\fB\fBITIMER_REALPROF\fR\fR
.ad
.RS 19n
Decrements in real time. It is designed to be used for real-time profiling of
multithreaded programs. Each time the \fBITIMER_REALPROF\fR timer expires, one
counter in a set of counters maintained by the system for each lightweight
process (lwp) is incremented. The counter corresponds to the state of the lwp
at the time of the timer tick. All lwps executing in user mode when the timer
expires are interrupted into system mode. When each lwp resumes execution in
user mode, if any of the elements in its set of counters are non-zero, the
\fBSIGPROF\fR signal is delivered to the lwp. The \fBSIGPROF\fR signal is
delivered before any other signal except \fBSIGKILL\fR. This signal does not
interrupt any in-progress function. A  \fBsiginfo\fR structure, defined in
\fB<sys/siginfo.h>\fR, is associated with the delivery of the \fBSIGPROF\fR
signal, and includes the following members:
.sp
.in +2
.nf
si_tstamp;      /* high resolution timestamp */
si_syscall;     /* current syscall */
si_nsysarg;     /* number of syscall arguments */
si_sysarg[\|];     /* actual syscall arguments */
si_fault;       /* last fault type */
si_faddr;       /* last fault address */
si_mstate[\|];     /* ticks in each microstate */
.fi
.in -2

The enumeration of microstates (indices into  \fBsi_mstate\fR) is defined in
\fB<sys/msacct.h>\fR.
.sp
Unlike the other interval timers, the \fBITIMER_REALPROF\fR interval timer is
not inherited across a call to one of the \fBexec\fR(2) family of functions.
.RE

.SH RETURN VALUES
.sp
.LP
Upon successful completion, \fB0\fR is returned. Otherwise, \fB\(mi1\fR is
returned and \fBerrno\fR is set to indicate the error.
.SH ERRORS
.sp
.LP
The \fBgetitimer()\fR and \fBsetitimer()\fR functions will fail if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The specified number of seconds is greater than 100,000,000, the number of
microseconds is greater than or equal to 1,000,000, or the \fIwhich\fR argument
is unrecognized.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR alarm (2),
.BR exec (2),
.BR gettimeofday (3C),
.BR sleep (3C),
.BR sysconf (3C),
.BR attributes (7),
.BR standards (7)
.SH NOTES
.sp
.LP
The \fBsetitimer()\fR function is independent of the \fBalarm\fR(2) and
\fBsleep\fR(3C) functions.
.sp
.LP
The \fBITIMER_PROF\fR and \fBITIMER_REALPROF\fR timers deliver the same signal
and have different semantics. They cannot be used together.
.sp
.LP
The granularity of the resolution of alarm time is platform-dependent.
